You're forgetting triple turn-ins. If one is say 700 gil, then that's potentially 3600 (700 x 3 turnins x 2 for HQ). That's only if you care about getting this achievement though. There are better ways of making pure net profit from trade leves, and the price point is lower than most people think (it's Quarrymill).
Regardless, almost anything is better than a mere 700ish on a single battlecraft leve.